The present invention relates to a preheating apparatus for scrap metal and, more particularly, to a louvered clamshell door assembly for a scrap metal charging bucket in a preheating apparatus.
Preheating assemblies are known in the iron and steel recycling industry for utilizing waste heat from freshly poured metal ingots, billets or molds to preheat scrap metal in preparation for melting. In the past, freshly poured ingots were simply removed from their molds and allowed to cool to the ambient air temperature before being subjected to further processing. Large amounts of heat were lost to the atmosphere during such cooling, inasmuch as iron ingots are typically removed from their molds at a temperature on the order of 1,000.degree. F. With rising energy costs and increasing concern for energy conservation, it has been recognized that the heat contained in freshly poured ingots can be profitably put to use to preheat scrap metal prior to melting.
Several alternative embodiments of scrap metal preheating assemblies are disclosed in U.S. Pat. No. 4,028,048 to Harrison R. Woolworth, the specification of which is hereby incorporated by reference for the purpose of background information. One embodiment of a preheating apparatus includes a double-walled scrap metal charging bucket which is mountable in an enclosure wherein hot ingots may be emplaced under the bucket. The charging bucket includes a clamshell door assembly which opens downwardly to empty the bucket and which forms a hemispherical bucket floor when closed. Woolworth teaches the modification of the otherwise conventional clamshell door assembly by providing multiple apertures in the central portion of the clamshell doors and multiple slots spaced around the periphery of the doors. The apertures in the central portion allow rising hot air to circulate upwardly through scrap metal resting on the clamshell doors. The slots around the periphery of the clamshell doors allow cool air from the upper interior of the charging bucket to descend by convection through convection channels between the double walls of the charging bucket.
In practice, it has been found that the apertures and slots disclosed in Woolworth impair the normal operation of the clamshell doors. Scrap metal pieces resting on the upper inside surfaces of the clamshell doors tend to become jammed in the apertures. This inhibits free opening of the doors, inasmuch as the doors must swing upwardly and outwardly in mutually opposite directions to allow the scrap metal pieces to slide off of the doors and downwardly through the opening. Jamming of scrap metal pieces in the apertures prevents free sliding of the scrap metal relative to the door surfaces and thus impairs opening of the door assembly.
Accordingly, it is an object and purpose of the present invention to provide a clamshell door assembly for a charging bucket which permits free circulation of rising hot air upwardly through the door assembly and yet also adequately retains and supports scrap metal contained in the charging bucket. It is also an object of the present invention to accomplish the foregoing objects without impairing in any way the normal mechanical operation of the clamshell doors. It is yet another object to provide a clamshell door assembly through which air can freely circulate and yet which can also withstand repeated heavy impacts during loading of scrap metal and the stress of repeated thermal contraction and expansion.